Every developer on the planet knows the first acronym. Very few know the next two. There are many other "What you see is..." phrases, but these three actually matter.
WYSIWYG — What You See Is What You Get: a style of software that supposedly allows users to see the end result of their work. As a replacement for command line control of the computer, WYSIWYG editors promised an intuitive, graphical user interface to create "content". The user gets a preview of what the end result will look like as they create their content. Bravo was the first WYSIWYG editor. It was developed in 1974, and it was the first time users had font options and text formatting in a word processor. These days, we should probably stop just copying 41 year old concepts and create something better.
WYSIWYNC — What You See Is What You Never Could: first coined by Ted Nelson, WYSIWYNC editors really show the limitations of WYSIWYG. Or, at least they would the software actually existed. 54 years after the development of Nelson's WYSIWYNC software, called Project Xanadu, it's yet to be completed. The problem with WYSIWYG is what comes after the 'G'. The full acronym should read: What You See Is What You Get... When You Print It Out. WYSIWYG editors create static content, that a user could simply print out. However, screens allow for dynamic content that can't be represented on paper. Decades after the first GUI, we are still using screens to mimic paper. The world has been waiting for Project Xanadu for so long, most have given up. For the remaining believers, as Nelson says, we fight on.
WYSIATI — What You See Is All There Is: coined by Daniel Kahneman and described in his book Thinking, Fast and Slow. A phrase used to describe a bias in reasoning and decision making: people only consider the information presented in front of them, or information they can easily recall. Rarely do they take the time to realize how little information they have while making a decision. Considering only what one knows, and not understanding how little they know, can lead to poorly formed conclusions.